1. Field of the Invention
The present invention relates to a carbon nano-tube (CNT) thin film treated with chemical having an electron withdrawing functional group and a manufacturing method thereof, and more particularly, to a CNT material treated with chemical having an electron withdrawing functional group to reduce a contact resistance between the CNTs and capable of increasing conductivity of an electrode prepared using the process, and a treating method thereof.
2. Description of the Prior Art
A transparent electrode that is transparent and allows electric current to conduct is necessary for a display device. Indium tin oxide (ITO) is currently most used for the electrode. Although the ITO is currently most used, the cost thereof is increased as the consumption of indium is increased. In particular, since the resistance is increased due to cracks occurring when the ITO electrode is bent, it is difficult to apply the ITO to a flexible device in future.
Accordingly, it is needed to develop a transparent electrode that can be applied to a flexible device. Regarding this, the CNT is most spotlighted in recent years. Since the CNT has excellent electric conductivity and strength and an easily flexible property, a flexible transparent electrode using the CNT can be widely applied, as electrode material, to energy devices such as solar cell and secondary cell as well as display devices such as LCD, OLED and paper-like display.
The most important properties required for the CNT transparent electrode include conductivity, transparency and flexibility. In general, the CNT transparent electrode is prepared by dispersing CNT powders in a solution including a dispersing agent to manufacture CNT ink and then applying the CNT ink on a plastic substrate. In order to increase the conductivity of the CNT transparent electrode, it is important for carriers to move through the CNT itself and to freely move between the CNT and the CNT.
According to the recent research, when an amount of CNT is enough for the CNT to contact each other in a transparent electrode having a CNT network structure, i.e., in a state of percolation threshold or more, the resistance of the CNT itself little influences on the CNT network film. To the contrary, the contact resistance between the CNT and the CNT has a main influence on the resistance of the CNT network film. Therefore, the formation of the CNT network and the decrease in the contact resistance between the CNT and the CNT are important for increase of the conductivity of the CNT transparent electrode.
The CNT is classified into metallic and semiconducting types. The CNT of armchair having no chirality is a metallic CNT having a bandgap of 0 and the CNT is again classified into metallic and semiconducting types depending on a degree of the chirality.
The chirality can be expressed in accordance with a wrapping direction in a carbon plate structure of the CNT. In coordinates of (n, m) indicating the direction, when n and m are multiples of 3, it is referred to as metallic. When n and m are not multiples of 3, it is referred to as semiconducting. In growing the CNT, it is probabilistically said that ⅓ or less of the entire CNTs is metallic and ⅔ or more of the entire CNTs is semiconducting. Since the metallic CNT of armchair is formed very rarely, the amount thereof may be negligible.
When a transparent electrode is formed with CNTs in which the CNTs of the above two types are mixed, a barrier is formed between the CNTs having different bandgaps and the electrons flow. Thereby, the contact resistance between the CNTs is increased to lower the conductivity of the entire CNTs. Therefore, when a transparent electrode is formed with CNTs in which the CNTs of the two types are mixed, it is necessary to lower the contact resistance between the CNTs having different bandgaps.